Hand tools of the pliers type having locking mechanisms to maintain the opposed jaws in a gripping position are well known. Typically such tools incorporate a fixed handle and jaw element and a movable jaw pivoted to the handle, operable by an attached movable handle.
After the jaw separation is coarsely adjusted, compression of the handles drives a toggle mechanism beyond a dead center point to a position where the jaws are locked onto the workpiece. This permits the tool to be maintained in a clamped position without the continued maintenance of manual pressure.
The toggle action is conventionally developed around three pivot points in the operating mechanism. The dead center point exists when the three pivot points are in a line. The line is called the "power line", and extends from a first pivot point joining the movable handle to the movable jaw, through a second, intermediate pivot in the toggle link mechanism between the handles, to a third pivot point at the other end of the toggle mechanism which is in contact with the fixed handle. Upon compressing the handles to close the jaws, the center pivot point is forced across the power line, maintaining the jaws in the closed position until the center pivot is forced back across the power line. Typically, this is performed with the assistance of a release lever.
The locking and unlocking functions may require a fair amount of manual effort to cause the toggle linkage pivot point to cross the power line, which increases as the compressive force locking the jaws increases. In particular, release of the tool from the workpiece is often accompanied by an almost explosive separation of the tool handles as the power line is crossed. Accordingly, a variety of mechanisms have been developed to lessen the necessary force, typically in conjunction with release of the tool, rather than during engagement of the tool about a workpiece. These mechanisms are often complicated, requiring additional levers and other elements between the handles. They often do not provide a satisfactory solution to the problems inherent in such locking tools.
It is accordingly an object of the present invention to provide an engagement and release mechanism for toggle lock tools which can operate with minimal applied force.
An additional object of the present invention is to provide an engagement and release mechanism in which the transfer across the power line is accomplished in a smooth and efficient manner, to avoid pinching, snapping and jerking of the tool.
Another object of the present invention is to provide an engagement mechanism which allows for increased gripping force to be applied by a given size tool.
Still another object of the present invention is to provide an engagement and release mechanism which is free of secondary mechanisms which can crowd the space between the handles, and which may be prone to interference with tool operation and which can be unintentionally operated, causing premature tool release.
An additional object is to reduce loss of gripping force as the center pivot passes the centerline into its locked position.
Yet a further object of the present invention is to provide an engagement and release mechanism which may be incorporated into tools with minimal cost.
A still further object of the present invention is to provide an engagement and release mechanism in combination with a grip handle, which may be of improved comfort to the user.